Answer:
Overriding a veto (Congress) and finding executive orders unconstitutional (Supreme Court)
Explanation:
If your question is open ended, then these are two options.
When Congress passes a bill to the President, he can either sign it into law, or veto it. Often, when Congress is of a different political party than the President, they can override his veto with 2/3 of the vote in Congress. It can eventually be checked by the Supreme Court.
However, if a President needs to get moving fast, or needs to run departments, he can sign executive orders. They aren't exactly laws, but they are enforced like them. However, if the President abuses this power, the Supreme Court can declare the order "unconstitutional."
Hoped that helped.
